microRNA (miRNA) is a class of small non-coding RNAs that suppress the expression of protein-encoding genes via translational repression and/or mRNA degradation. Studies indicate that miRNAs act as global regulators of cellular functions, through their involvement in a wide range of physiological and pathological processes including cancer development. In a genetic screen, we found that miR-30, a miRNA frequently overexpressed in cancer, disrupts a critical tumor suppressing mechanism called oncogene-induced senescence. Further studies demonstrated that miR-30 disrupts oncogenic ras-induced senescence by directly targeting CHD7, a transcriptional co-activator, and TNRC6A, an RNA-binding protein essential for miRNA functionality. In this grant application, we will investigate te mechanisms underlying the roles of CHD7 and TNRC6A in miR-30-mediated bypass of oncogenic ras-induced senescence, and examine the impact of the miR-30-CHD7/TNRC6A regulatory circuit on cancer development in vivo. In Aim 1, we will investigate the hypothesis that CHD7 acts as a transcriptional coactivator to induce the transcription of a key senescence effector p16INK4A, and that by suppressing CHD7, miR-30 inhibits ras-induced p16INK4A expression and hence senescence induction. Alternative approaches are proposed to perform ChIP-seq analysis to systematically identify additional direct transcriptional targets of CHD7 involved in senescence. In Aim 2, the hypothesis will be tested that by suppressing TNRC6A, miR-30 globally down-regulates the functionality of miRNAs, which in turn leads to disruption of ras-induced senescence. In Aim 3, we will analyze the effect of miR-30 on senescence induction and cancer development in vivo using miR-30 transgenic mice and a mouse cancer model. In addition, the expression levels of miR-30, CHD7 and TNRC6A will be determined in human tumor samples, in order to establish that miR-30 contributes to human cancer development by suppressing its direct targets CHD7 and TNRC6A. Studies proposed in this grant will provide mechanistic insights into the novel function of miR-30 in oncogene-induced senescence. Through analyses of these miR-30 targets, we will identify novel mechanisms and novel signaling components that mediate oncogene-induced senescence and tumor suppression, which will offer new opportunities for cancer therapies targeting cellular senescence.